Concepts of time on Earth, Space and on other Planets

Main Question or Discussion Point

I have information that time slows down in space. For example if an astronaut is on the Moon or in space for one year, he didn't age. If he returns to Earth he is as young as he left Earth? I don't understand this.

If someone travels to another planet (3 months journey through space), I believe he must get older 3 months, or not? And why not?

He reached his destination, the other planet and decides to stay for 10 years. After 10 years he travels back to Earth. I am sure people on the other planet (as there might be intelligent life) would age as we do. So he must be 10 years older after 10 years. Hence, if he return to Earth, he must be 10 years older like everyone else on Earth.

If you now about the concept of time on other planets and in space, please explain. Does it mean in space time does not exist, so in space no creature will age? I am sure on other planets creatures get old and die too, like on Earth.

I have information that time slows down in space. For example if an astronaut is on the Moon or in space for one year, he didn't age. If he returns to Earth he is as young as he left Earth? I don't understand this.

Maybe you heard of the twin paradox? This is a real physical effect from special relativity, but it requires that the astronaut travels close to the speed of light, turns around and comes back. And even in this case, the astronaut gets older - just slower than we on earth.

For regular space travel (everything we did so far and everything planned for the future), this effect is negligible.

I have information that time slows down in space. For example if an astronaut is on the Moon or in space for one year, he didn't age. If he returns to Earth he is as young as he left Earth? I don't understand this.

If someone travels to another planet (3 months journey through space), I believe he must get older 3 months, or not? And why not?

He reached his destination, the other planet and decides to stay for 10 years. After 10 years he travels back to Earth. I am sure people on the other planet (as there might be intelligent life) would age as we do. So he must be 10 years older after 10 years. Hence, if he return to Earth, he must be 10 years older like everyone else on Earth.

If you now about the concept of time on other planets and in space, please explain. Does it mean in space time does not exist, so in space no creature will age? I am sure on other planets creatures get old and die too, like on Earth.

Note that ALL effects of time dilation are VERY VERY minor to the point of being almost unmeasurable here on Earth, and even for things moving in space the effect is still so small that it has almost no effect on anything we do. All of our interplanetary probes and our Moon missions do not need to account for it.

@Astrid: I think you misunderstood what you read a little. I think that article meant moving close to the speed of light? Then yes, time will pass slower for that person. This means that a person sleeping and not moving in space would not age slower.

If you think about it, being in space cannot mean time passing slower. Firstly, Earth is already in space. But time still passes nicely for us. And although gravity decreases with Distance, but if you are a finite distance away, gravity is not 0, it is just very weak. So what do you exactly define as space?

Edit: And you can't possibly define space as vacuum, because what special property does vacuum have such that time slows down or even stop there?